This series was motivated by the discussion in this thread: https://www.redhat.com/archives/libvir-list/2017-June/msg01370.html
The issue this series addresses is that when libvirt unplugs a VFIO PCI device, it may attempt to bind the host device back to the host driver when QEMU emits the DEVICE_DELETED event for the corresponding vfio-pci device. However, the VFIO group FD is not actually cleaned up until vfio-pci device is *finalized* by QEMU, whereas the event is emitted earlier during device_unparent. Depending on the host device and how long certain operations like resetting the device might take, this can in result in libvirt trying to rebind the device back to the host while it is still in use by VFIO, leading to host crashes or other unexpected behavior. In particular, Mellanox CX4 adapters on PowerNV hosts might not be fully quiesced by vfio-pci's finalize() routine until up to 6s after the DEVICE_DELETED was emitted, leading to detach-device on the libvirt side pretty much always crashing the host. Implementing this change requires 2 prereqs to ensure the same information is available when the DEVICE_DELETED is finally emitted: 1) Storing the path in the composition patch, which is addressed by PATCH 1, which was plucked from another pending series from Greg Kurz: https://lists.gnu.org/archive/html/qemu-devel/2017-07/msg07922.html since we are now "disconnected" at the time the event is emitted, and 2) Deferring qemu_opts_del of the DeviceState->QemuOpts till finalize, since that is where DeviceState->id is stored. This was actually how it was done in the past, so PATCH 2 simply reverts the change which moved it to device_unparent. >From there it's just a mechanical move of the event from device_unparent to device_finalize. Since this was originally posted a kernel fix was merged to address the race on the kernel side (6586b561), but it would still be good to fix this on the QEMU side for older host kernel and for clearer semantics on the libvirt/management side. v3: - rebased on master - fixed comment typo in PATCH 1 (Eric Blake) v2: - rebased on master - fixed up inaccurate comment in PATCH 1 (Eric Auger) hw/core/qdev.c | 31 ++++++++++++++++++++----------- include/hw/qdev-core.h | 1 + 2 files changed, 21 insertions(+), 11 deletions(-)
